Flexible tool joint

ABSTRACT

A flexible tool joint for use in a drill string having a housing and a mandrel connected therein and providing a discontinuity in strength of the drill string, said tool joint comprising concentrically disposed tubular members having adjacent ends adapted for connection to the drill string, the inner one of said members having its other end adapted for connection to said mandrel, said members being laterally spaced throughout a substantial portion of their lengths so that said inner member can bend independently of said outer member, and coengageable shoulder surfaces on said members for preventing separation thereof in the event of failure of said inner member.

United States Patent Kisling, III et a].

FLEXIBLE TOOL JOINT Inventors: James W. Kisling, HI, Houston; Benjamin P. Nutter, Bellville, both Primary Examiner-William E. Wayner Attorney-Emest R. Archambeau, .lr., Stewart F. Moore, David L. Moseley, Edward M. Roney and William R. Sherman of Tex.

[73] Assignee: Schlumberger Technology Corpora- [57] ABSTRACT New York A flexible tool joint for use in a drill string having a {22] Filed: Dec. 9, 1970 housing and a mandrel connected therein and providing a discontinuity in strength of the drill string, said [21] Appl 96499 tool joint comprising concentrically disposed tubular members having adjacent ends adapted for connection 52 U.S. c1. ..64/23, 175/293 to the drill string. the inner one of said members 511 m or. ..Fl6d 3/06, F2lb 1/06 s its 9 end wanted for connection to Said 58 Field of Search...175/320 x, 293; 173/128, 131; 9 hem! l 138]09; 64/23 substantial portion of their lengths so that said mner member can bend independently of said outer [56] Ram and member, and ooengageable shoulder surfaces on said members for preventing separation thereof in the UNITED STATES PATENTS event of failure of said inner member.

3,323,327 6/1967 Leathers et al ..64/23 2,953,351 9/1960 Bodine et a] ..l75/293 X 1] Claims, 4 Drawing Figures 1 58 F 1 7 3 60:1/ 3 62 1 67 L l 56 5/ l l e 4! 50 l l I 1 FLEXIBLE TOOL JOINT This invention relates to a flexible tubular structure that may be used, for example, in combination with a drilling jar in a well bore to minimize fatigue stress and wear on parts of the jar during rotary drilling operations.

A well tool such as a drilling jar usually comprises telescopically disposed mandrel and housing members that are slidably splined together and connected in the string of drill collars above the bit. Since the jar housing generally has the same outer diameter as the drill collars, the mandrel is necessarily of smaller size and is thus normally the weakest member in the drill string. During rotary drilling operations, torque is of course transmitted through the jar, and under usual circumstances where the drilled hole is not perfectly plumb, the stresses in the mandrel will vary between tension and compression during each revolution of the drill string, tending to cause undesirable wear on the mandrel and perhaps even fatigue failure thereof, as well as wear on the seal packing that is normally disposed between the mandrel and the housing.

It is the general object of the present invention to provide a new and improved flexible tool joint that may be used, for example, in combination with a well jar to minimize wear and stress on the jar mandrel and the seal packing during rotation in a well bore.

This and other objects are attained in accordance with the concepts of the present invention through the provision of an elongated tubular structure including an inner member having one end adapted to be connected to a jar mandrel, and an outer member extending longitudinally along the inner member in laterally spaced relationship thereto so that the inner member is somewhat flexible. The outer member has the same outer diameter as the drill string in which the structure is connected, and the outer end of the inner member as well as the adjacent end of the outer member are adapted to be rigidly connected to the drill string. One or more spacers are disposed in the annular cavity between the two members to limit lateral flexure of the inner member, and opposed shoulder surfaces are provided on the inner and the outer members to prevent longitudinal separation of said members in the event that the inner member should fail during drilling operations. Surfaces on the inner and outer members are longitudinally aligned for engagement under compressive loading to prevent buckling of the inner member.

The present invention has other objects and advantages which will become more fully apparent in connection with the following detailed description. The structure and operation of the present invention may be best understood with reference to the drawings, in which:

FIG. 1 is a somewhat schematic view of a flexible joint in accordance with this invention being used with a well jar during rotary drilling operations in a well bore;

FIG. 2 is an enlarged longitudinal sectional view, with portions in side elevation of the flexible joint structure of FIG. 1;

FIG. 3 is a cross-section taken on line 33 of FIG. 2; and

FIG. 4 is a cross-sectional view with portions in side elevation of a modified form of the present invention.

Referring initially to FIG. I, a borehole 10 is shown being drilled through earth formations by using conventional rotary drilling techniques. A drill bit 11 is attached to the lower end of a drill string that includes a number of heavy drill collars 12 to provide the necessary weight on the bit. A drilling jar 13 can be selectively connected in the drill collar string preferably near the upper end of the string but with several drill collars located between the jar and the drill pipe that extends upwardly to the surface.

The jar 13 generally includes a tubular housing 20 that is telescopically disposed over a tubular mandrel 21, the housing being threadedly connected at 22 to the drill collar thereabove. The mandrel 21 has a central bore 23 that continues the drilling fluid circulation path through the drill string. The housing 20 is movable to some extent in both longitudinal directions along the mandrel 21 from a central or cocked position, upward movement causing one hammer" provided by an inwardly extending shoulder surface 24 to strike an anvil" provided by an outwardly extending shoulder surface 25 on the mandrel, downward movement causing another hammer surface 26 to strike a second anvil surface 27. The impact force in either direction is transmitted by the mandrel 21 to stuck tools therebelow. The housing 20 and the mandrel 21 have coengaging splines 29 for transmitting torque and rotation through the jar during drilling operations. A seal packing 30 prevents drilling fluids from entering in between the housing 20 and the mandrel 21 at their lower ends, whereas a floating or compensating seal packing unit 31 is used to prevent fluids from entering at their upper ends. The vacant spaces between the housing 20 and the mandrel 21 are filled with a typical lubricating oil or the like.

A tripping mechanism indicated generally at 32 is disposed in between upper and lower resilient structures 33 and 34 and functions to restrain longitudinal movement of the housing 20 in either direction from the cocked or intermediate position to enable energy to be stored in the drill pipe before the jar hits to intensify the jarring action. The details of the tripping mechanism 32 form no part of this invention are fully disclosed and claimed in copending application, Ser. No. 82,284, Kisling, filed Oct. 20, 1970 and assigned to the assignee of this invention. Briefly, however, the tripping mechanism 32 includes an annular expansible and contractive latch sleeve 35 having internal threads that grip external threads on the mandrel 21, the sleeve being held engaged with the mandrel by locking surfaces on a locking sleeve 36. Upon a preselected extent of longitudinal movement of the housing 20 along the mandrel 21, such movement being resisted by the resilient structures 33 or 34, the sleeve member 35 is released for outward movement so that the housing 20 can move freely along the mandrel 21 until a hammer encounters an anvil to effect a jarring action. The tripping mechanism 32 can be recocked by moving the housing 20 in the opposite direction so that jarring blows can be repeatedly struck in either direction until the stuck object is driven loose.

The lower end of the mandrel 21 extending downwardly from the lower end of the housing 20 is connected to the upper end of the flexible joint structure 40 that is constructed in accordance with the principles of the present invention. As shown in greater detail in FIG. 2, the flexible joint structure includes an inner tubular member 41 having a threaded pin portion 42 at its upper end for connection to the lower end of the jar mandrel 21. An outer tubular member 43 extends longitudinally along the inner member 41, its upper end surface 44 terminating short of a downwardly facing shoulder surface 45 on the pin portion 42, its lower end having a threaded pin portion 46 for connection to the drill collars therebelow and an internal threaded section 47 to which the lower end of the inner member 41 is connected. The inner wall surface 48 of the outer member 43 is laterally spaced from the outer wall surface 49 of the inner member 41 to provide an annular cavity 50 therebetween. Upper and lower spacers 51 and 52 are fitted snugly around the inner member 41, the upper spacer 51 being disposed near the upper end of the outer member 43, the lower spacer 52 being located at approximately the mid point of the cavity 50. Typical drill pipe protectors made of relatively hard synthetic rubber or the like can be used as the spacers 51 and 52, and there is lateral clearance between the outer surface of each spacer and the inner wall of the outer member 43. Several wash ports 53 are provided through the wall of the outer member 43 at the lower end of the cavity 50 so that settlements in the drilling fluids can exit the cavity.

The upper end portion of the outer member 43 is constituted by a collar 55 that is threaded to the member 43 at 56, the upper portion of the collar being inwardly thickened and provided with an internal annular recess 57. The recess 57 receives an annular stop ring 58 that is radially split at 59 as shown in FIG. 3, with the lower surface 60 of the stop ring being longitudinally aligned for engagement with an upwardly facing surface 61 on an external annular shoulder 62 provided on the inner member 41.

In operation, the flexible joint structure 40 is connected between the jar mandrel 21 and the drill collars 12 therebelow and lowered into the borehole for drilling operations. It should be noted that the inner member 41 has a lesser wall thickness than the wall thickness of the jar mandrel 21 protruding from the lower end of the jar housing 20, so that the inner member 21 has the least amount of stiffness of any tubular member in the drill string. In crooked or otherwise deviated boreholes, the members are subjected to some bending during rotation, so that the stresses therein alternate between tension and compression stress during each revolution of the drill string. Such varying stresses could heretofore cause a significant amount of wear on the jar mandrel 21 and the seal packing 30, with the risk that the seal packing would easily wear out or the mandrel part in two due to fatigue failure, however the use of the flexible joint structure 40 with its relative flexible inner member 41 serves to substantially isolate the jar mandrel 21 from such stresses. Should bending of the inner member 21 exceed a certain normal amount, the spacers 51 and 52 engage inner wall surfaces of the outer member 43 so that the outer member attributes to the total stiffness of the flexible joint structure. The lateral clearance between the upper spacer 51 and the adjacent inner wall surface of the outer member 43 is sized with respect to the lateral clearance between the stop ring 58 and the inner member 41 such that the spacer 51 will engage the outer member 43 during bending and prevent the stop ring 58 from rubbing against the adjacent peripheral surface of the member 41.

The vertical clearance space previously mentioned between the upper end of the collar 55 and the shoulder 44 on the inner member 41 is selected such that as downward jarring action is being applied to the drill string, the surfaces 44 and 45 will engage and force will be transmitted through the outer member 43 before the inner member 41 can be foreshortened enough in compression to cause buckling thereof.

As a safety factor in the event that the inner member 41 should be twisted ofl' during use, the stop ring 58 will engage the shoulder surface 61 on the inner member to prevent separation of the inner and outer members. Thus it is practically impossible in the event of a twist off to be faced with a fishing operation to retrieve the drill collar string below the jar and flex joint.

A modified form of the safety device discussed immediately above is shown in FIG. 4. In this embodiment, the upper end portion of the collar 55 is longitudinally slotted at circumferentially spaced points to divide the portion into a plurality of resilient fingers 65, each having its upper end portion inwardly thickened sufliciently to provide a stop surface 66 that will engage the stop surface 61 on the inner member 41. Thus formed, the fingers can be spread outwardly during assembly to pass over the annular shoulder 62, and then resile inwardly thereabove, whereupon a continuous retaining band 67 is positioned around the fingers to prevent outward flexure thereof.

It will now be apparent that a new and improved flexible joint structure has been provided for use in combination with a well jar to wear on the jar parts during rotary drilling operations. Although the joint structure has been illustrated and described in conjunction with a jar, it will be appreciated that the joint could be used with any downhoie tool where there is a discontinuity in strength in the drill string, for example, tools having tubular telescoping members such as slip joints or bumper subs.

Since certain changes or modifications may be made in the disclosed embodiments by those skilled in the art without departing from the inventive concepts involved, it is the aim of the appended claims to cover all such changes and modifications falling within the true spirit and scope of the present invention.

We claim:

1. Apparatus for use in combination with a well tool having a mandrel disposed within a housing and subject to rotation in a well bore, comprising: an inner tubular member having one end adapted to be connected to said mandrel; an outer tubular member extending longitudinally along said inner member and laterally spaced therefrom to provide an annular cavity therebetween extending substantially throughout the length of said outer member so that said inner member can bend within limits independently of said outer member; and means for connecting the other end of said inner member and one end of said outer member to a drill string, said outer member having substantially the same outer diameter as said housing, said inner member having no greater stiffness than said mandrel.

2. The apparatus of claim 1 further including axially aligned stop means on said members for preventing separation thereof in a well bore.

3. The apparatus of claim 2 wherein said stop means includes opposed shoulder surfaces on said inner member and said outer member.

4. The apparatus of claim 3 wherein one of said opposed shoulder surfaces is provided by an annular split ring disposed within a recess on one of said members.

5. The apparatus of claim 1 further including means disposed in said cavity for limiting the amount of bending of said inner member with respect to said outer member.

6. The apparatus of claim 5 wherein said limiting means includes at least one annular ring mounted on said inner member and being sized to provide a clearance space between the external surface thereof and the adjacent wall of said cavity.

'7. Apparatus for use in combination with a well too] having a mandrel telescopically disposed within a housing and subject to bending stress during rotation in a well bore, comprising: concentric tubular members having adjacent ends joined to one another and adapted for connection to a drill string, the inner one of said members having its other end adapted for connection to said mandrel, said members being transversely sized to have lateral clearance substantially throughout their lengths so that said inner member can bend within limits independently of said outer member, said other end of said inner member having a thickened crosssection beyond the adjacent end of said outer member to provide axially aligned transverse surfaces on said members, said surfaces being normally in spaced relationship but adapted to be brought together by compression force applied to said inner member, engagement of said surfaces limiting the compression force on said inner member to prevent buckling thereof.

8. The apparatus of claim 7 further including comgageable stop means on said inner and outer members to prevent separation thereof.

9. The apparatus of claim 8 wherein said stop means includes opposed shoulder surfaces on said members located adjacent said other end of said inner member.

10. The apparatus of claim 9 wherein one of said opposed shoulder surfaces is provided by an annular split ring disposed within a recess on one of said members.

11. The apparatus of claim 8 wherein said stop means includes an annular shoulder on said inner member, resilient fingers 0n the adjacent end portion of said outer member and having inwardly thickened portions to provide shoulder surfaces engageable with said annular shoulder, and retaining means for preventing outward flexure of said fingers. 

1. Apparatus for use in combination with a well tool having a mandrel disposed within a housing and subject to rotation in a well bore, comprising: an inner tubular member having one end adapted to be connected to said mandrel; an outer tubular member extending longitudinally along said inner member and laterally spaced therefrom to provide an annular cavity therebetween extending substantially throughout the length of said outer member so that said inner member can bend within limits independently of said outer member; and means for connecting the other end of said inner member and one end of said outer member to a drill string, said outer member having substantially the same outer diameter as said housing, said inner member having no greater stiffness than said mandrel.
 2. The apparatus of claim 1 further including axially aligned stop means on said members for preventing separation thereof in a well bore.
 3. The apparatus of claim 2 wherein said stop means includes opposed shoulder surfaces on said inner member and said outer member.
 4. The apparatus of claim 3 wherein one of said opposed shoulder surfaces is provided by an annular split ring disposed within a recess on one of said members.
 5. The apparatus of claim 1 further including means disposed in said cavity for limiting the amount of bending of said inner member with respect to said outer member.
 6. The apparatus of claim 5 wherein said limiting means includes at least one annular ring mounted on said inner member and being sized to provide a clearance space between the external surface thereof and the adjacent wall of said cavity.
 7. Apparatus for use in combination with a well tool having a mandrel telescopically disposed within a housing and subject to bending stress during rotation in a well bore, comprising: concentric tubular members having adjacent ends joined to one another and adapted for connection to a drill string, the inner one of said members having its other end adapted for connection to said mandrel, said members being transversely sized to have lateral clearance substantially throughout their lEngths so that said inner member can bend within limits independently of said outer member, said other end of said inner member having a thickened cross-section beyond the adjacent end of said outer member to provide axially aligned transverse surfaces on said members, said surfaces being normally in spaced relationship but adapted to be brought together by compression force applied to said inner member, engagement of said surfaces limiting the compression force on said inner member to prevent buckling thereof.
 8. The apparatus of claim 7 further including coengageable stop means on said inner and outer members to prevent separation thereof.
 9. The apparatus of claim 8 wherein said stop means includes opposed shoulder surfaces on said members located adjacent said other end of said inner member.
 10. The apparatus of claim 9 wherein one of said opposed shoulder surfaces is provided by an annular split ring disposed within a recess on one of said members.
 11. The apparatus of claim 8 wherein said stop means includes an annular shoulder on said inner member, resilient fingers on the adjacent end portion of said outer member and having inwardly thickened portions to provide shoulder surfaces engageable with said annular shoulder, and retaining means for preventing outward flexure of said fingers. 